The legally required electronic cryptograms known as digital signatures were some of the key technologies that made the Internet an opportunity for business. The digital signatures not only authenticate the identity of a person but also assurance the legitimacy of the information attached to the signature, be it a credit card number, an order form or a written document. Digital signatures reduce the costs of the commercial process through the Internet. Digital signatures are based on public key cryptography, it uses a public key algorithm.
Digital signatures generate two keys that are precisely linked: one private and one public. To produce a digital signature, signing software, such as an email solution creates a one-way hash of the electronic data to be signed. The private key is used to encrypt the hash. The encrypted hash along with other information, such as the hashing algorithm is the digital signature.
The main purpose for encrypting the hash instead of the entire message or document is that a hash function can convert an input into a fixed value, which is usually shorter. This saves time since hashing is much faster than signing.